This invention relates in general to ball valves and improved seals for such valves. More particularly, the invention relates to such valves which incorporate all-metal component parts.
In general, ball valves are relatively low-cost devices which may be changed from an open to a closed position or vice versa with only a quarter turn of the ball-controlling handle. The ball plug typically has a full bore therethrough and the valve is designed to provide unimpeded flow through the full bore with a minimum of pressure drop. The ball plug-controlling handle indicates the open-to-closed position of the valve such that the degree of flow can be ascertained by looking at the handle position. The ball plug is supported within the center of the valve flow passageway by top and bottom annular seats. These seats perform the function of sealing off the remainder of the valve from the self-wiping action as the ball plug rotates. This self-wiping action prevents the buildup of contamination which might impede full closure of the valve.
Due to the fact that the bulk of flow control does not occur within a minor movement of the handle, such valves are well suited for certain types of flow control and have relatively good throttling characteristics at low flow conditions. Typically, in order to provide a good sealing characteristics around the ball plug, the annular seats are often fabricated from a polymeric material such as elastic rubber or polyethylene compounds. These types of material offer the advantage of being deformable at moderately low pressure levels so that machining and/or molding tolerances can be relaxed over what would be required for harder materials, and the resultant sealing face will still conform to the ball plug surface contour which it contacts.
Other seals which may be used within the valve are typically conventional rubber O-ring-type seals which offer similar advantages of relaxed tolerances and the ability to readily adapt to the surfaces against which they are to seal. One disadvantage to the use of such synthetic materials within this type of valve is that the valve will often not be acceptable for the transfer of certain types of fluids and will be limited by what upper temperature it can withstand without performance being adversely affected. High-temperature situations may occur either by means of the exterior environment into which he particular valve may be placed or by the nature of the fluid which is being controlled and routed by the valve. However, since the majority of such valves is constructed of metal, even if the exterior atmosphere is at standard conditions, heat conduction from a high-temperature fluid passing through the valve will result in the entire valve being at an elevated temperature. Therefore, for either of these high-temperature situations to which the valve may be subjected, rubber and synthetic compounds are generally not acceptable.
The following list of patents provides a sampling of ball valve designs which have been conceived in an effort to try and overcome one or more of the particular disadvantages which a certain style of ball valve might have, depending on the intended application.
______________________________________ Pat. No. Patentee Issue Date ______________________________________ 3,722,856 Koch et al. 3/27/73 4,066,881 Gaillard 2/08/77 3,617,025 Gerbic 11/02/71 3,960,363 Domyan 6/01/76 3,717,323 Geipel 2/20/73 3,520,512 Huber 7/14/70 3,549,122 Graham 12/22/70 3,669,406 Moore 6/13/72 2,297,161 Newton 9/29/42 3,218,024 Kroekel 11/16/65 3,266,769 Shand 8/16/66 2,837,308 Shand 6/03/58 3,542,335 Scaramucci 11/24/70 3,207,524 Trbovich 9/21/65 ______________________________________
Koch et al. discloses a ball valve with separate end fittings which permit the valve to serve as a union without disturbing the valve member. O-rings are used to facilitate sealing between the valve body and the end fittings and two seat-defining rings engage the exterior of the ball about the inlet and outlet flow passages.
Gaillard discloses a fluid-tight packing for closure devices such as ball valves which are designed to be compressed between two components of the device. The packing is cut from a sheet of carbonaceous material which retains its effectiveness at temperatures in the order of 600 degrees Centigrade.
Gerbic discloses a ball valve with retractable rings wherein the seat rings may be retracted for free, incremental operation of the valve. It is suggested that with conventional ball valves the drag of the seat ring against the ball renders its virtually impossible to achieve precision control. The drag may be alleviated by retracting the seat rings while the valve is being operated.
Domyan discloses a ball valve with an actuator wherein a seal assembly with a combination O-ring swivel and seal for producing a tight seal is hidden in a pocket isolated from the flow of fluid through the valve by an inlet reentrant flange and the valve body. The ball valve also includes a spring which urges the seal of the assembly against the spherical surfaces of the ball.
Geipel discloses a ball valve having a novel seat arrangement wherein the seat rings, placed on opposite sides of the ball closure member, are each retained by a ferrule which is screwed into the valve body. The annular valve seats are formed of a yieldable, resilient material and are retained against a shoulder in the valve body by the tightening action of the ferrules.
Graham discloses a sealed ball valve wherein a rotatable valve controls the rate of fluid flow therethrough and is engaged by a sealing means which includes annular members of different materials and rigidity adjacently spaced to each other and engaging the ball. Specifically, split annular discs are stacked together in tetrafluoroethylene resin such that ball pressure under a closed condition will cause the sealing means to yield rather than deforming the ball. However, with the arrangement of individual annular rings, it appears that uniform and proper positioning of each ring individually would be difficult to achieve without extensive manufacturing time and expense. Furthermore, maintaining suitable full sealing contact of these various rings against the ball plug surface would appear to be quite difficult.
Moore discloses a ball valve wherein an annular seal is held in place by an edge-anchored annular retainer. The retainer is oversized for the valve housing and on installation resides in a state of compression.
Newton discloses a seat ring for ball valves wherein a concavo-convex ring of flexible elastic material is mounted within the valve casing and provides the seat ring. Upon assembly with the closure member, a greater bearing load is provided at the outer periphery of the seat ring.
Kroekel discloses a fluid motor-actuated ball valve wherein the ball valve may be opened at a preselected speed. The design disclosed is a ball valve adjusting screw and lock nut which set the vertical height of the ball and includes bellows for adjusting the pressure of sealing at different seal locations.
Shand ('769) discloses a fluid contrtol valve having rockable sealing means. As disclosed by FIG. 4, one of the sealing arrangements includes a bellows member which is sealed to a tubular member which in turn seals against the ball plug. Connection 16 in combination with casing 11 clamps the bellows member in place.
Shand ('308) discloes a fluid control valve wherein the seal against the ball plug is achieved by a combination of parts. This combination includes a seating ring, diaphragm, a metal ring member and a contact spring.
Scaramucci discloses a valve seal which is continually biased toward the valve member. In most of the arrangements disclosed, the seal is created by means of an elastomer member pressing against the ball plug, an L-shaped ring acting on the elastomer member and a tensioning member acting on the L-shaped ring.
Trbovich discloses a seal which is generally V-shaped in transverse section. This shape enables the ends to be compressed together when in use, yet flex outwardly with expansion or positional shifting of the two members between which the seal is disposed.
In addition to the fact that typical ball valves are limited in their application by the fluid being conducted and the operating temperature range, such valves also possess a further disadvantage when they are not provided with spring tension means in order to maintain the annular seats in direct sealing contact with the ball plug. Designs which merely clamp the polymeric seat members against the ball plug do not provide means for adjusting the pressure on the annular seats so that sealing contact can be preserved as the continued use of the ball valve gradually wears down the annular seats or loosens their fit against the ball plug. Although certain ball valve designs may include materials for the seats which are somewhat temperature-resistant, such as disclosed by the Graham patent, which includes metal rings and a polytetrafluoroethylene resin, these same devices also typically incorporate O-rings as part of the seal between the valve body and the ball plug stem. Therefore, although the flow passageway may be somewhat temperature-resistant and the sealing of the seat to the ball plug maintained over elevated temperature ranges, the entire device is not suitable for use in an elevated temperature environment due to the presence of the synthetic rubber material used fore the O-rings.
The Gaillard patent discloes a valve device which is designed and intended for high-temperature application while still preserving fluid-tightness. However, the valve device incorporates a graphite ring between the connecting flange and the valve body, and since the connecting flange forces the ball plug seal seats against the ball plug, there is no spring tension by which fluid-tight sealing can be preserved during the life of the valve.